Аннотация:Photoionisation occurs when an extreme ultraviolet (XUV) or x-raypulse interacts with an atom. Using intense XUV light pulses deliveredby Free Electron Lasers, several photons can be sequentiallyabsorbed, determining the emission of multiple photoelectronsand the generation of highly charged ions. We demonstrate that,exploiting the unique properties of polarization control and tunabilityof FERMI, the complete characterization of the two-photon, doubleionization process can be achieved.https://www.elettra.trieste.it/science/highlights.html